Photomask blank, photomask, and methods of manufacturing the same

ABSTRACT

A photomask blank is for use in manufacturing a photomask to be applied with exposure light having a wavelength of 200 nm or less. The photomask blank has a light-transmitting substrate and a light-shielding film formed thereon. The light-shielding film has a light-shielding layer containing a transition metal and silicon and a front-surface antireflection layer formed contiguously on the light-shielding layer and made of a material containing at least one of oxygen and nitrogen. The light-shielding film has a front-surface reflectance of a predetermined value or less for the exposure light and has a property capable of controlling the change width of the front-surface reflectance at the exposure wavelength to be within 2% when the thickness of the front-surface antireflection layer changes in the range of 2 nm. The material of the front-surface antireflection layer having a refractive index n and an extinction coefficient k capable of achieving such property is selected.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a Divisional of application Ser. No. 13/126,614 filed Apr. 28,2011, claiming priority based on International Application No.PCT/JP2009/068359 filed on Oct. 27, 2009, which claims priority fromJapanese Patent Application No. 2008-278918 filed Oct. 29, 2008, thecontents of all of which are incorporated herein by reference in theirentirety.

TECHNICAL FIELD

This invention relates to a photomask blank and a photomask for use inthe manufacture of semiconductor devices or the like and to methods ofmanufacturing the same, and so on.

BACKGROUND ART

The miniaturization of semiconductor devices and the like isadvantageous in bringing about an improvement in performance andfunction (higher-speed operation, lower power consumption, etc.) and areduction in cost and thus has been accelerated more and more. Thelithography technique has been supporting this miniaturization andtransfer masks are a key technique along with exposure apparatuses andresist materials.

In recent years, the development of the half-pitch (hp) 45 nm to 32 nmgenerations according to the semiconductor device design rule has beenprogressing. This corresponds to ¼ to ⅙ of a wavelength 193 nm of ArFexcimer laser exposure light. Particularly in the hp45 nm and subsequentgenerations, only the application of the resolution enhancementtechnology (RET) such as the conventional phase shift method, obliqueillumination method, and pupil filter method and the optical proximitycorrection (OPC) technique is becoming insufficient, and the hyper-NAtechnique (immersion lithography) and the double exposure (doublepatterning) technique are becoming necessary.

SUMMARY OF THE INVENTION Problem to be Solved by the Invention

Normally, in the case of manufacturing a photomask having a mask patternof a light-shielding film on a transparent substrate, the mask patternis transferred by dry-etching the light-shielding film using as a mask aresist film formed with the mask pattern. In this event, the resist filmis also etched to be consumed. In order to improve the resolution whenthe mask pattern is transferred to the light-shielding film, the resistfilm should remain with a predetermined thickness or more after the dryetching. However, if the thickness of the resist film is made thicker,there arises a problem of the collapse of the resist pattern and,therefore, it is not desirable to increase the film thickness.

In order to improve the resolution upon the transfer to thelight-shielding film, it is effective to reduce the thickness of thelight-shielding film. However, if the thickness of the light-shieldingfilm is reduced, the OD value (optical density) decreases.

In JP-A-2006-78807 (Patent Document 1), in order to reduce the thicknessof a light-shielding film, use is made of a transition metal silicidematerial with an absorption coefficient greater than that of achromium-based material and, particularly in terms of the dryetchability, molybdenum silicide is described to be preferable. By this,the thickness of the light-shielding film can be made thinner thanconventional.

In the meantime, normally, a light-shielding film of a mask blank has anat least two-layer structure of a front-surface antireflection layer anda light-shielding layer or a three-layer structure of a front-surfaceantireflection layer, a light-shielding layer, and a back-surfaceantireflection layer. The front-surface antireflection layer is designedsuch that the front-surface reflectance for exposure light becomesoptimal with its thickness at a stage immediately after the manufactureof a photomask.

However, after the manufacture of the photomask, the occurrence of filmloss of the front-surface antireflection layer cannot be prevented inthe course of repeating photomask cleaning (ozone water cleaning or thelike). Conventionally, not so much consideration is given to a change infront-surface reflectance due to the film loss of the front-surfaceantireflection layer. Particularly when a molybdenum silicide basedmaterial is used as the front-surface antireflection layer, the tendencyof the film loss due to the photomask cleaning is significant.

The front-surface reflectance of the photomask is most affected by theproperties (parameters) of the front-surface antireflection layer. Thechange in thickness of the front-surface antireflection layer tends toaffect the front-surface reflectance. In a process of forming thefront-surface antireflection layer in manufacturing processes of themask blank, the front-surface antireflection layer is formed to athickness as designed, but since the thickness of the front-surfaceantireflection layer is as thin as about 10 nm to 20 nm, it is difficultto form the front-surface antireflection layer to the designed thicknessso that there may occur a difference in thickness of about 1 nm from thedesigned thickness.

There has been a problem that in the case where the film design iscarried out without considering the change width of the front-surfacereflectance due to the thickness, when the thickness of thefront-surface antireflection layer deviates from the designed value asdescribed above, the front-surface reflectance increases.

It is an object of this invention to provide a photomask blank having alight-shielding film which is capable of controlling the change width ofa front-surface reflectance to be small with respect to a change inthickness of a front-surface antireflection layer.

Means for Solving the Problem

Various aspects of this invention will be described hereinbelow.

(Aspect 1)

A photomask blank for use in manufacturing a photomask adapted to beapplied with exposure light having a wavelength of 200 nm or less,wherein the photomask blank comprises a light-transmitting substrate anda light-shielding film formed on the light-transmitting substrate, thelight-shielding film comprises a light-shielding layer containing atransition metal and silicon, and a front-surface antireflection layerformed above and in contact with the light-shielding layer and made of amaterial containing at least one of oxygen and nitrogen, thelight-shielding film has a front-surface reflectance of a predeterminedvalue or less for the exposure light and has a property capable ofcontrolling a change width of the front-surface reflectance at theexposure wavelength to be within 2% when a thickness of thefront-surface antireflection layer is changed in a range of 2 nm, and aselection is made of the material of the front-surface antireflectionlayer having a refractive index n and an extinction coefficient k whichcan achieve the property.

(Aspect 2)

The photomask blank according to aspect 1, wherein the refractive indexn of the front-surface antireflection layer is greater than 1.5 and 3.0or less and the extinction coefficient k of the front-surfaceantireflection layer is 0.3 or more and 1.5 or less.

(Aspect 3)

The photomask blank according to aspect 1 or 2, wherein thefront-surface reflectance of the light-shielding film at the exposurewavelength is 25% or less.

(Aspect 4)

The photomask blank according to any of aspects 1 to 3, wherein thethickness of the front-surface antireflection layer is 20 nm or less.

(Aspect 5)

The photomask blank according to any of aspects 1 to 4, wherein thelight-shielding layer is formed of a material substantially comprisingmolybdenum and silicon.

(Aspect 6)

The photomask blank according to any of aspects 1 to 5, wherein thetransition metal of the light-shielding layer is molybdenum and themolybdenum content is 20 at % or more and 40 at % or less.

(Aspect 7)

The photomask blank according to any of aspects 1 to 6, wherein thefront-surface antireflection layer further contains silicon.

(Aspect 8)

The photomask blank according to aspect 7, wherein the front-surfaceantireflection layer further contains molybdenum.

(Aspect 9)

The photomask blank according to any of aspects 1 to 8, wherein thelight-shielding film comprises a back-surface antireflection layerformed under and in contact with the light-shielding layer andcontaining at least one of oxygen and nitrogen and silicon.

(Aspect 10)

The photomask blank according to any of aspects 1 to 9, wherein thelight-shielding film has a thickness of 60 nm or less.

(Aspect 11)

A photomask blank for use in manufacturing a photomask adapted to beapplied with exposure light having a wavelength of 200 nm or less,wherein the photomask blank comprises a light-transmitting substrate anda light-shielding film formed on the light-transmitting substrate, thelight-shielding film comprises a light-shielding layer containing atransition metal and silicon and a front-surface antireflection layerformed above and in contact with the light-shielding layer and made of amaterial containing at least one of oxygen and nitrogen, thelight-shielding film has a front-surface reflectance of 25% or less forthe exposure light and has a property capable of controlling a changewidth of the front-surface reflectance at the exposure wavelength to bewithin 3% when a thickness of the front-surface antireflection layer ischanged in a range of 2 nm, and a selection is made of the material ofthe front-surface antireflection layer having a refractive index n andan extinction coefficient k which can achieve the property.

(Aspect 12)

The photomask blank according to aspect 11, wherein the refractive indexn of the front-surface antireflection layer is 1.4 or more and 2.9 orless and the extinction coefficient k of the front-surfaceantireflection layer is 0.4 or more and 1.3 or less.

(Aspect 13)

The photomask blank according to aspect 11 to 12, wherein the thicknessof the front-surface antireflection layer is 20 nm or less.

(Aspect 14)

The photomask blank according to any of aspects 11 to 13, wherein thelight-shielding layer is formed of a material substantially comprisingmolybdenum, silicon, and nitrogen.

(Aspect 15)

The photomask blank according to any of aspects 11 to 14, wherein thetransition metal of the light-shielding layer is molybdenum and themolybdenum content is 9 at % or more and 40 at % or less.

(Aspect 16)

The photomask blank according to any of aspects 11 to 15, wherein thefront-surface antireflection layer further contains molybdenum andsilicon.

(Aspect 17)

The photomask blank according to any of aspects 11 to 16, wherein thelight-shielding film has a thickness of 60 nm or less.

(Aspect 18)

A method of manufacturing the photomask blank according to any ofaspects 1 to 17, comprising

obtaining relationships between thickness and front-surface reflectanceof front-surface antireflection layers with respect to a predeterminedlight-shielding layer by changing a refractive index n and an extinctioncoefficient k of the front-surface antireflection layers to a pluralityof values, and

selecting, from the obtained relationships, a combination of a thicknesschange range, n, and k of the front-surface antireflection layer havinga property capable of controlling a change width of the front-surfacereflectance to a predetermined value or less with respect to a change inthickness in a predetermined range, and using the selected combination.

(Aspect 19)

A photomask manufactured using the photomask blank according to any ofaspects 1 to 17.

(Aspect 20)

A method of manufacturing a photomask, using the photomask blankaccording to any of aspects 1 to 17.

(Aspect 21)

A semiconductor device manufacturing method of manufacturing asemiconductor device by transferring a pattern of the photomaskaccording to aspect 19.

Effect of the Invention

According to this invention, it is possible to provide a photomask blankhaving a light-shielding film which is capable of controlling the changewidth of a front-surface reflectance to be small with respect to achange in thickness of a front-surface antireflection layer even in thecase where the thickness of the front-surface antireflection layer ischanged from a designed thickness thereof due to a film formation errorin a film forming process in the manufacture of the mask blank or thethickness of the front-surface antireflection layer is reduced due tomask cleaning or the like after the manufacture of a photomask from themask blank.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exemplary cross-sectional view showing one example of aphotomask blank according to Example 1 of this invention.

FIG. 2 is an exemplary cross-sectional view for explaining manufacturingprocesses of a photomask according to Example 1 of this invention.

FIG. 3 is a diagram obtained in Example 1 of this invention and showingthe relationships between the thickness and the front-surfacereflectance of front-surface antireflection layers when the refractiveindex n of the front-surface antireflection layers is fixed while theextinction coefficient k thereof is changed to a plurality of values.

FIG. 4 is a diagram obtained in Example 1 of this invention and showingthe relationships between the thickness and the front-surfacereflectance of front-surface antireflection layers when the refractiveindex n of the front-surface antireflection layers is set to a valuedifferent from that in FIG. 3 while the extinction coefficient k thereofis changed to the plurality of values.

FIG. 5 is a diagram obtained in Example 1 of this invention and showingthe relationships between the thickness and the front-surfacereflectance of front-surface antireflection layers when the refractiveindex n of the front-surface antireflection layers is set to a valuedifferent from those in FIGS. 3 and 4 while the extinction coefficient kthereof is changed to the plurality of values.

FIG. 6 is a diagram obtained in Example 1 of this invention and showingthe relationships between the thickness and the front-surfacereflectance of front-surface antireflection layers when the refractiveindex n of the front-surface antireflection layers is set to a valuedifferent from those in FIGS. 3, 4, and 5 while the extinctioncoefficient k thereof is changed to the plurality of values.

FIG. 7 is a diagram obtained in Example 1 of this invention and showingthe relationships between the thickness and the front-surfacereflectance of front-surface antireflection layers when the refractiveindex n of the front-surface antireflection layers is set to a valuedifferent from those in FIGS. 3, 4, 5, and 6 while the extinctioncoefficient k thereof is changed to the plurality of values.

FIG. 8 is a diagram obtained in Example 1 of this invention and showingthe relationships between the thickness and the front-surfacereflectance of front-surface antireflection layers when the refractiveindex n of the front-surface antireflection layers is set to a valuedifferent from those in FIGS. 3, 4, 5, 6, and 7 while the extinctioncoefficient k thereof is changed to the plurality of values.

FIG. 9 is a diagram showing the relationship between the molybdenumcontent and the optical density per unit thickness in a thin film in theform of a MoSi film.

FIG. 10 is a diagram showing the reflection and transmission spectra ofa light-shielding film obtained in Example 1 of this invention.

FIG. 11 is a diagram obtained in Example 3 of this invention and showingthe relationships between the thickness and the front-surfacereflectance of front-surface antireflection layers when the refractiveindex n of the front-surface antireflection layers is fixed while theextinction coefficient k thereof is changed to a plurality of values.

FIG. 12 is a diagram obtained in Example 3 of this invention and showingthe relationships between the thickness and the front-surfacereflectance of front-surface antireflection layers when the refractiveindex n of the front-surface antireflection layers is set to a valuedifferent from that in FIG. 11 while the extinction coefficient kthereof is changed to the plurality of values.

FIG. 13 is a diagram obtained in Example 3 of this invention and showingthe relationships between the thickness and the front-surfacereflectance of front-surface antireflection layers when the refractiveindex n of the front-surface antireflection layers is set to a valuedifferent from those in FIGS. 11 and 12 while the extinction coefficientk thereof is changed to the plurality of values.

FIG. 14 is a diagram obtained in Example 3 of this invention and showingthe relationships between the thickness and the front-surfacereflectance of front-surface antireflection layers when the refractiveindex n of the front-surface antireflection layers is set to a valuedifferent from those in FIGS. 11, 12, and 13 while the extinctioncoefficient k thereof is changed to the plurality of values.

FIG. 15 is a diagram obtained in Example 3 of this invention and showingthe relationships between the thickness and the front-surfacereflectance of front-surface antireflection layers when the refractiveindex n of the front-surface antireflection layers is set to a valuedifferent from those in FIGS. 11, 12, 13, and 14 while the extinctioncoefficient k thereof is changed to the plurality of values.

FIG. 16 is a diagram obtained in Example 3 of this invention and showingthe relationships between the thickness and the front-surfacereflectance of front-surface antireflection layers when the refractiveindex n of the front-surface antireflection layers is set to a valuedifferent from those in FIGS. 11, 12, 13, 14, and 15 while theextinction coefficient k thereof is changed to the plurality of values.

Mode for Carrying out the Invention

Hereinbelow, embodiments of this invention will be described.

A photomask blank according to the first embodiment of this invention isa photomask blank for use in manufacturing a photomask which is adaptedto be applied with exposure light having a wavelength of 200 nm or less.The photomask blank comprises a light-transmitting substrate and alight-shielding film formed on the light-transmitting substrate, whereinthe light-shielding film comprises a light-shielding layer containing atransition metal and silicon and a front-surface antireflection layerformed above and in contact with the light-shielding layer and made of amaterial containing at least one of oxygen and nitrogen and thelight-shielding film (thus, the front-surface antireflection layer andthe light-shielding layer) has a front-surface reflectance of apredetermined value or less for the exposure light and has a propertycapable of controlling the change width of the front-surface reflectanceat the exposure wavelength to be within 2% when the thickness of thefront-surface antireflection layer is changed in the range (changewidth) of 2 nm.

According to the above-mentioned first embodiment, it is possible toprovide the photomask blank having the light-shielding film which iscapable of controlling the change width of the front-surface reflectanceto be small with respect to a change in thickness of the front-surfaceantireflection layer. As a consequence, the change in front-surfacereflectance (particularly the increase in front-surface reflectance) dueto the occurrence of film loss can be suppressed to be small in thecourse of repeating photomask cleaning (ozone water cleaning or thelike) after the manufacture of the photomask.

Further, even when the thickness of the front-surface antireflectionlayer immediately after the formation thereof deviates (e.g. about 2 nm)from a designed value, the change in front-surface reflectance(particularly the increase in front-surface reflectance) caused by thedifference in thickness from the designed thickness can be suppressed tobe small.

In the above-mentioned first embodiment, the light-shielding film (thus,the front-surface antireflection layer and the light-shielding layer)has the property that the change in front-surface reflectance is 1%/nmwith respect to a change in thickness of the front-surfaceantireflection layer.

A photomask blank according to the second embodiment of this inventionis also a photomask blank for use in manufacturing a photomask which isadapted to be applied with exposure light having a wavelength of 200 nmor less. The photomask blank comprises a light-transmitting substrateand a light-shielding film formed on the light-transmitting substrate,wherein the light-shielding film comprises a light-shielding layercontaining a transition metal and silicon and a front-surfaceantireflection layer formed above and in contact with thelight-shielding layer and made of a material containing at least one ofoxygen and nitrogen and the light-shielding film (thus, thefront-surface antireflection layer and the light-shielding layer) has afront-surface reflectance of 25% or less for the exposure light and hasa property capable of controlling the change width of the front-surfacereflectance at the exposure wavelength to be within 3% when thethickness of the front-surface antireflection layer is changed in therange of 2 nm.

According to the above-mentioned second embodiment, it is possible toprovide the photomask blank having the light-shielding film which iscapable of controlling the change width of the front-surface reflectanceto be small with respect to a change in thickness of the front-surfaceantireflection layer. When the front-surface reflectance is set to aslow as 25% or less, the allowable change width can be set to 3%. As aconsequence, the change in front-surface reflectance (particularly theincrease in front-surface reflectance) due to the occurrence of filmloss can be suppressed to be small in the course of repeating photomaskcleaning (ozone water cleaning or the like) after the manufacture of thephotomask.

Further, even when the thickness of the front-surface antireflectionlayer immediately after the formation thereof deviates (e.g. about 2 nm)from a designed value, the change in front-surface reflectance(particularly the increase in front-surface reflectance) caused by thedifference in thickness from the designed thickness can be suppressed tobe small.

In the above-mentioned second embodiment, the light-shielding film(thus, the front-surface antireflection layer and the light-shieldinglayer) has the property that the change in front-surface reflectance is1.5%/nm with respect to a change in thickness of the front-surfaceantireflection layer.

As described above, the light-shielding film (thus, the front-surfaceantireflection layer and the light-shielding layer) has the propertycapable of controlling the change width of the front-surface reflectanceto be within 2% or within 3% when the thickness of the front-surfaceantireflection layer is changed in the range (change width) of 2 nm. Asa material of the front-surface antireflection layer, a selection ismade of a material having n and k which can control the change width ofthe front-surface reflectance to be within 2% or within 3% when thethickness of the front-surface antireflection layer is changed in therange of 2 nm. A selection may also be made of a material of thefront-surface antireflection layer having n and k such that, with thepredetermined front-surface reflectance or less, the change width of thefront-surface reflectance becomes the predetermined value or less withrespect to a change in thickness, in the predetermined range, of thefront-surface antireflection layer formed on the light-shielding layer.A selection may also be made of a material of the front-surfaceantireflection layer having n and k such that, with the predeterminedfront-surface reflectance or less, the change width of the front-surfacereflectance becomes the predetermined value or less with respect to achange in thickness (a change in thickness from a designed value in thefilm formation or a change in thickness in the manufacture of a mask orin the use thereof) in the predetermined range (the respective layersare controlled so that the change width of the front-surface reflectancebecomes the predetermined value or less). A selection may also be madeof a material (a combination of a thickness change range, n, and k) ofthe front-surface antireflection layer having a property capable of,with the predetermined front-surface reflectance or less, controllingthe change width of the front-surface reflectance to the predeterminedvalue or less with respect to a change in thickness in the predeterminedrange. A selection may also be made of a material (a combination of athickness change range, n, and k) of the front-surface antireflectionlayer in terms of a predetermined material (a combination of n and k) ofthe light-shielding layer.

The design concept of n and k described above is different from, forexample, the design concept of n and k that gives priority tosignificantly reducing the front-surface reflectance.

The thickness change range of the front-surface antireflection layer canbe selected, for example, in the thickness range of greater than 10 nmand 20 nm or less (further, 10 nm or more and 15 nm or less) of thefront-surface antireflection layer, as an arbitrary range (e.g. athickness range of 10 nm or more and 12 nm or less, a thickness range of13 nm or more and 15 nm or less, a thickness range of 18 nm or more and20 nm or less, or the like) in which the thickness changes in the range(change width) of 2 nm.

The design thickness of the front-surface antireflection layer can bearbitrarily determined in the above-mentioned thickness range. Forexample, it can be set to a middle value or to an upper limit value inconsideration of film loss, or, in consideration of a film formationerror (e.g. 1 nm), it can be set on a lower limit side, corresponding tothe film formation error, from the upper limit value.

In a graph showing the relationship between the thickness and thefront-surface reflectance of a front-surface antireflection layer withrespect to a predetermined light-shielding layer (further in a graphgroup obtained by changing n and k, respectively), a selection is madeof a combination of a thickness change range, n, and k of thefront-surface antireflection layer corresponding to a portion (thicknessrange) where the change in front-surface reflectance is small withrespect to a change in thickness, i.e. visually a flat portion with asmall angle between itself and the thickness (abscissa axis) in thegraph, and use is made of the selected combination.

For example, graphs showing the relationships between the thickness andthe front-surface reflectance of front-surface antireflection layerswith respect to a predetermined light-shielding layer are obtained bychanging the refractive index n and the extinction coefficient k of thefront-surface antireflection layers to a plurality of values, then aselection is made, from the graphs obtained above, of a combination of athickness change range, n, and k of the front-surface antireflectionlayer having a property capable of controlling the change width of thefront-surface reflectance to a predetermined value or less with respectto a change in thickness in a predetermined range, and use is made ofthe selected combination.

More specifically, for example, first, a material of a light-shieldinglayer is fixed (in this event, n and k of the light-shielding layer aredetermined), then n and k of a front-surface antireflection layer arefixed, and a graph A showing the relationship between the thickness andthe front-surface reflectance of the front-surface antireflection layeris obtained by optical simulation (e.g. k=1.2 in FIG. 3 (graph 1)).Similarly, graphs B are obtained by fixing n while changing k (e.g.k=0.3, 0.6, 0.9, 1.5, and 1.8 in FIG. 3 (graph 1)). Similarly to thegraphs B, graphs C are obtained by changing n (a graph group of FIGS. 3to 8 (graphs 1 to 6)). From this graph group C, a selection is made of amaterial of the front-surface antireflection layer (a combination of athickness change range, n, and k of the front-surface antireflectionlayer) having a property capable of controlling the change width of thefront-surface reflectance to a predetermined value or less with respectto a change in thickness in a predetermined range, and use is made ofthe selected combination. In this event, it is possible to select thecombination which minimizes the change width of the front-surfacereflectance, and to use the selected combination.

As described above, in the total of 36 kinds, i.e. 6 kinds (6 levels) ofchange in k and 6 kinds (6 levels) of change in n, those kindssatisfying the above-mentioned predetermined conditions are specified,then those kinds satisfying conditions required for a light-shieldingfilm such as a predetermined OD or higher over the entirelight-shielding film are further specified, and then, among them, themost preferable kind is selected. Thus, it is not easy to find out theone that satisfies such selection conditions of this invention.

Each of the above-mentioned first and second embodiments is differentfrom the design concept that gives priority to significantly reducingthe front-surface reflectance. For example, in the case of estimating afilm loss of 2 nm and selecting and using a thickness range of 13 nm to15 nm in a curve of k=1.2 in FIG. 6 (graph 4) (n=2.36), even if thethickness changes in this range, the front-surface reflectance remainsabout 21% and thus the change width of the front-surface reflectance issuppressed to about 1%. As described above, by obtaining the graphs A,B, or C, a selection may be made of a material of the front-surfaceantireflection layer (a combination of a thickness change range, n, andk of the front-surface antireflection layer) having a property capableof controlling the change width of the front-surface reflectance to apredetermined value or less with respect to a change in thickness in apredetermined range.

In each of the above-mentioned first and second embodiments, 36 kinds ofgraphs are produced by carrying out optical simulations with n and keach changed in 6 levels. If more graphs are produced by carrying outoptical simulations with n and k each changed in more levels, to therebyselect a material of the front-surface antireflection layer, thematerial selection accuracy is further improved.

The front-surface antireflection layer preferably has a refractive indexn of greater than 1.5 and 3.0 or less and an extinction coefficient k of0.3 or more and 1.5 or less.

In general, the front-surface reflectance for exposure light having awavelength of 200 nm or less (ArF excimer laser exposure light or thelike) is set to at least 30% or less. Therefore, it is preferable toselect a material of the front-surface antireflection layer (acombination of a thickness change range, n, and k of the front-surfaceantireflection layer) adapted to provide a front-surface reflectance of30% or less and having a property capable of controlling the changewidth of the front-surface reflectance to be within 2% when thethickness of the front-surface antireflection layer is changed in therange of 2 nm. When a study is made of a material of the front-surfaceantireflection layer satisfying the above-mentioned conditions on thebasis of the respective graphs in FIGS. 3 to 8, it is seen that amaterial group with a refractive index n of 1.5 does not satisfy theconditions to a degree and thus is inadequate (but, if slightlyexceeding 1.5, there is a material group that satisfies the conditions).In material groups with a refractive index n of up to 3.0, there arematerials that satisfy the conditions. On the other hand, even in amaterial group with an extinction coefficient k of 0.3, there arematerials that satisfy the conditions. A material group with anextinction coefficient k of 1.8 does not satisfy the conditions and,even if falling slightly below 1.8, the conditions are not satisfied. Ina material group with an extinction coefficient k of 1.5, there arematerials that satisfy the conditions. Based on the study describedabove, a selection is made of the above-mentioned ranges of therefractive index n and the extinction coefficient k which are preferablefor a material to be used as the front-surface antireflection layer.

A material containing a transition metal and silicon (including atransition metal silicide) is used as the light-shielding layer. As theusable transition metal, there can be cited molybdenum, tantalum,tungsten, titanium, chromium, hafnium, nickel, vanadium, zirconium,ruthenium, rhodium, or the like, and one or two or more kinds of themmay be added to silicon.

The front-surface reflectance of the light-shielding film is preferably25% or less.

The front-surface reflectance of 30% is a minimal numerical value and,in order to make the front-surface antireflection more effective, thefront-surface reflectance for the exposure light is preferably set to25%.

For example, a selection is made of a material of the front-surfaceantireflection layer with n and k having a property such that thelight-shielding film has a front-surface reflectance of 25% or less andthe change width of the front-surface reflectance is within 2% when thethickness of the front-surface antireflection layer is changed in therange of 2 nm.

When a study is made of a material of the front-surface antireflectionlayer satisfying such conditions by the same technique on the basis ofthe respective graphs in FIGS. 3 to 8, it is seen that a selection maybe made of a material having a refractive index n of 1.8 or more and 3.0or less and an extinction coefficient k of 0.3 or more and 1.2 or less.

The front-surface antireflection layer preferably has a refractive indexn of 1.4 or more and 2.9 or less and an extinction coefficient k of 0.4or more and 1.3 or less.

When the front-surface reflectance for exposure light having awavelength of 200 nm or less (ArF excimer laser exposure light or thelike) is 25% or less, it is possible to select a material of thefront-surface antireflection layer (a combination of a thickness changerange, n, and k of the front-surface antireflection layer) having aproperty capable of controlling the change width of the front-surfacereflectance to be within 3% when the thickness of the front-surfaceantireflection layer is changed in the range of 2 nm.

When a study is made of a material of the front-surface antireflectionlayer satisfying the above-mentioned conditions on the basis ofrespective graphs in FIGS. 11 to 16, in a material group with arefractive index n of 1.4, there are materials that satisfy theconditions in the ranges where the extinction coefficient k is 0.7 to1.0 and the thickness is 14 to 20 nm. In a material group with arefractive index n of 1.7, there are materials that satisfy theconditions in the ranges where the extinction coefficient k is 0.4 to1.0 and the thickness is 13 to 20 nm. In a material group with arefractive index n of 2.0, there are materials that satisfy theconditions in the ranges where the extinction coefficient k is 0.4 to1.3 and the thickness is 10 to 20 nm. In a material group with arefractive index n of 2.31, there are materials that satisfy theconditions in the ranges where the extinction coefficient k is 0.4 to1.3 and the thickness is 8 to 20 nm. In a material group with arefractive index n of 2.6, there are materials that satisfy theconditions in the ranges where the extinction coefficient k is 0.4 to1.0 and the thickness is 8 to 20 nm. In a material group with arefractive index of 2.9, there are materials that satisfy the conditionsin the ranges where the extinction coefficient k is 0.4 to 1.0 and thethickness is 8 to 17 nm.

On the other hand, in a material group with an extinction coefficient kof 0.4, there are materials that satisfy the conditions in the rangeswhere the refractive index n is 1.7 to 2.9 and the thickness is 8 to 20nm. In a material group with an extinction coefficient k of 0.7, thereare materials that satisfy the conditions in the ranges where therefractive index n is 1.4 to 2.9 and the thickness is 8 to 20 nm. In amaterial group with an extinction coefficient k of 1.0, there arematerials that satisfy the conditions in the ranges where the refractiveindex n is 1.4 to 2.9 and the thickness is 8 to 20 nm. In a materialgroup with an extinction coefficient k of 1.3, there are materials thatsatisfy the conditions in the ranges where the refractive index n is 2.0to 2.31 and the thickness is 15 to 20 nm. In material groups withextinction coefficients k of 1.6 and 1.9, there is no material thatsatisfies the conditions.

Based on the study described above, a selection is made of theabove-mentioned ranges of the refractive index n and the extinctioncoefficient k which are preferable for a material to be used as thefront-surface antireflection layer.

Further, when the front-surface reflectance for the exposure light is25% or less, it is preferable to select a material having a propertycapable of controlling the change width of the front-surface reflectanceat the exposure wavelength to be within 2% when the thickness of thefront-surface antireflection layer is changed (reduced) in the range of2 nm.

When a study is made of a material of the front-surface antireflectionlayer satisfying the above-mentioned conditions on the basis of therespective graphs in FIGS. 11 to 16, in a material group with arefractive index n of 1.4, there are materials that satisfy theconditions in the ranges where the extinction coefficient k is 1.0 andthe thickness is 17 to 20 nm. In a material group with a refractiveindex n of 1.7, there are materials that satisfy the conditions in theranges where the extinction coefficient k is 0.7 to 1.0 and thethickness is 15 to 20 nm. In a material group with a refractive index nof 2.0, there are materials that satisfy the conditions in the rangeswhere the extinction coefficient k is 0.4 to 1.3 and the thickness is 12to 20 nm. In a material group with a refractive index n of 2.31, thereare materials that satisfy the conditions in the ranges where theextinction coefficient k is 0.4 to 1.3 and the thickness is 10 to 20 nm.In a material group with a refractive index n of 2.6, there arematerials that satisfy the conditions in the ranges where the extinctioncoefficient k is 0.4 to 1.0 and the thickness is 8 to 20 nm. In amaterial group with a refractive index of 2.9, there are materials thatsatisfy the conditions in the ranges where the extinction coefficient kis 0.4 to 1.0 and the thickness is 8 to 14 nm.

On the other hand, in a material group with an extinction coefficient kof 0.4, there are materials that satisfy the conditions in the rangeswhere the refractive index n is 2.0 to 2.9 and the thickness is 8 to 20nm. In a material group with an extinction coefficient k of 0.7, thereare materials that satisfy the conditions in the ranges where therefractive index n is 1.7 to 2.9 and the thickness is 8 to 20 nm. In amaterial group with an extinction coefficient k of 1.0, there arematerials that satisfy the conditions in the ranges where the refractiveindex n is 1.4 to 2.9 and the thickness is 8 to 20 nm. In a materialgroup with an extinction coefficient k of 1.3, there are materials thatsatisfy the conditions in the ranges where the refractive index n is 2.0to 2.31 and the thickness is 15 to 20 nm. In material groups withextinction coefficients k of 1.6 and 1.9, there is no material thatsatisfies the conditions.

From the study described above, it is seen that, as a material which isused as the front-surface antireflection layer and satisfies theabove-mentioned conditions, a selection may be made of a material havinga refractive index n of 1.4 or more and 2.9 or less and an extinctioncoefficient k of 0.4 or more and 1.3 or less.

The thickness of the front-surface antireflection layer is preferably 20nm or less.

Only in terms of controlling the change width of the front-surfacereflectance to the predetermined value or less, a considerably widerange of materials (a very wide range of combinations of n and k) can beused by increasing the thickness of the front-surface antireflectionlayer. However, the front-surface antireflection layer is part of thelight-shielding film and the extinction coefficient k of thefront-surface antireflection layer is much smaller than the extinctioncoefficient k of the light-shielding layer, and therefore, the ratio ofits contribution to the absorption coefficient of the entirelight-shielding film is low. As a consequence, even if the thickness ofthe front-surface antireflection layer is increased, the thickness ofthe light-shielding layer cannot be reduced correspondingly. In view ofthe above, the thickness of the front-surface antireflection layerforming part of the light-shielding film is preferably 20 nm or less.

The thickness of the front-surface antireflection layer is preferably 10nm or more and 20 nm or less and more preferably 12 nm to 17 nm.

The light-shielding layer is preferably formed of a materialsubstantially comprising molybdenum and silicon (including molybdenumsilicide).

The light-shielding layer is preferably formed of a materialsubstantially comprising molybdenum, silicon, and nitrogen. This isbecause the light-shielding layer is required to have a predetermined ODor higher in terms of reducing the thickness of the light-shielding filmand thus it is preferable to use the material containing molybdenum andsilicon, which has high light-shielding performance.

In the light-shielding layer substantially comprising molybdenum andsilicon, the molybdenum content is preferably 20 at % or more and 40 at% or less. This is because the light-shielding layer is required to havea predetermined OD or higher in terms of reducing the thickness of thelight-shielding film and thus it is preferable that the light-shieldinglayer be a metal film in the form of a MoSi film and that the Mo contentbe set to 20 at % or more and 40 at % or less.

Specifically, as shown in FIG. 9, if the molybdenum content is 20 at %or more, the optical density can be set to ΔOD=0.082 nm⁻¹@193.4 nm ormore, which is thus preferable.

In the case of the light-shielding layer in the form of the MoSi film inwhich the molybdenum content is 20 at % or more and 40 at % or less, thepresent inventors have found that, as shown in FIG. 9, it is possible toobtain the light-shielding layer having a relatively highlight-shielding property for ArF excimer laser exposure light ascompared with compositions (the molybdenum content is less than 20 at %or greater than 40 at %) outside of this range, that even if thethickness of the light-shielding layer is 40 nm or less which is muchsmaller than conventional, a predetermined light-shielding property(optical density) is obtained, and further that, by combining it with afront-surface antireflection layer and a back-surface antireflectionlayer each having a light-shielding property equal to conventional, thelight-shielding property (optical density 2.8 or more, preferably 3 ormore) sufficient for a light-shielding film of a photomask for ArFexcimer laser exposure is obtained.

In the light-shielding layer substantially comprising molybdenum,silicon, and nitrogen, the molybdenum content is preferably 9 at % ormore and 40 at % or less.

In the case of the MoSiN film in which the molybdenum content is 9 at %or more and 40 at % or less, the present inventors have found that, byadjusting the nitrogen content, it is possible to obtain thelight-shielding layer having a high optical density per unit thicknessand having a relatively high light-shielding property for ArF excimerlaser exposure light, that even if the thickness of the light-shieldinglayer is 50 nm or less, a predetermined light-shielding property(optical density) is obtained, and further that, by combining it with afront-surface antireflection layer having a light-shielding propertyequal to conventional, the light-shielding property (optical density 2.8or more, preferably 3 or more) sufficient for a light-shielding film ofa photomask for ArF excimer laser exposure is obtained.

Using the light-shielding layer having the above-mentioned predeterminedcomposition, the following functions and effects are obtained by areduction in thickness of the light-shielding layer (reduction inthickness of a transfer pattern due to a reduction in thickness of thelight-shielding film).

1) It is possible to achieve prevention of the collapse of the transferpattern in mask cleaning.

2) With the reduction in thickness of the light-shielding layer, theside wall height of the transfer pattern is also reduced and, therefore,the pattern accuracy particularly in the side wall height direction isimproved so that the CD accuracy (particularly the linearity) can beenhanced.

3) With respect to a photomask particularly for use in the hyper-NA(immersion) generation, it is necessary to reduce the thickness of atransfer pattern (reduce the side wall height of a transfer pattern) asa shadowing measure and this requirement can be satisfied.

The film containing molybdenum and silicon has a problem that when themolybdenum content is high, the chemical resistance and the cleaningresistance (particularly, alkaline cleaning or hot water cleaning)decrease. The molybdenum content is preferably set to not greater than40 at % which can ensure the required minimum chemical resistance andcleaning resistance when used as a photomask. As is also clear from FIG.9, while increasing the molybdenum content, the light-shieldingperformance of the MoSi film reaches a predetermined upper limit value.Since molybdenum is a rare metal, the molybdenum content is preferablyset to 40 at % or less also in terms of the cost.

If a material with a somewhat high extinction coefficient k is selectedas the front-surface antireflection layer, it is possible for thefront-surface antireflection layer to somewhat contribute to the OD ofthe entire light-shielding film. In this case, a material with ΔOD=0.08nm⁻¹@193.4 nm or more may be selected as the light-shielding layer sothat the content of molybdenum in the light-shielding layer in the formof the MoSi film can be set to 15 at % or more.

The light-shielding layer comprising molybdenum and silicon (MoSi film)represents a light-shielding layer substantially composed of molybdenumand silicon (including a metallic film substantially free of oxygen,nitrogen, etc. and a film made of a molybdenum silicide metal). Herein,being substantially free of oxygen and nitrogen includes a case in whichoxygen and nitrogen are each less than 5 at % with respect to thecomponents in the light-shielding layer).

Properly speaking, in terms of the light-shielding performance, it ispreferable not to contain these elements in the light-shielding layer.However, since these elements are often incorporated as impurities atthe stage of film forming processes, photomask manufacturing processes,or the like, the incorporation of such elements is allowed within arange not substantially affecting a reduction in light-shieldingperformance.

Further, other elements (carbon, boron, helium, hydrogen, argon, xenon,etc.) may be contained in the light-shielding layer in the form of theMoSi film within a range not impairing the properties and the functionsand effects described above. The thickness of the light-shielding layeris preferably 30 nm to less than 40 nm and more preferably 30 nm to 35nm. The light-shielding layer comprising molybdenum, silicon, andnitrogen (MoSiN film) represents a light-shielding layer substantiallycomposed of molybdenum, silicon, and nitrogen (including a film made ofa molybdenum silicide compound). For the same reason as that for theabove-mentioned MoSi film, the case where the film is substantially freeof oxygen includes an aspect in which oxygen is contained in a rangecapable of obtaining the functions and effects of this invention (theoxygen component is less than 5 at % in the light-shielding layer).Further, other elements (carbon, helium, hydrogen, argon, xenon, etc.)may be contained in the light-shielding layer in the form of the MoSiNfilm within a range not impairing the properties and the functions andeffects described above.

When the light-shielding layer contains nitrogen, the light-shieldingfilm can have the two-layer structure by giving a back-surfaceantireflection function to the light-shielding layer. Further, theetching rate of the light-shielding layer can be reduced as comparedwith the MoSi film, i.e. the light-shielding layer free of nitrogen.Therefore, as compared with the light-shielding film of the three-layerstructure having the light-shielding layer in the form of the MoSi film,the difference in etching rate between the antireflection layer and thelight-shielding layer can be reduced and thus the cross-sectional shapeof a pattern can be made better. The content of nitrogen in the MoSiNfilm is preferably less than 40 at %. When the nitrogen content is lessthan 40 at %, the thickness of the light-shielding layer can be madesmall so that the light-shielding film can be set to 60 nm or less.

The thickness of the light-shielding layer in the form of the MoSiN filmis preferably 40 nm or more and 50 nm or less. The front-surfaceantireflection layer preferably further contains silicon (including asilicide compound). Further, the front-surface antireflection layerpreferably contains molybdenum. As a material of the front-surfaceantireflection layer, use can be made of an oxide, a nitride, or anoxynitride composed mainly of one or two or more kinds of transitionmetals selected from molybdenum, tantalum, tungsten, titanium, chromium,hafnium, nickel, vanadium, zirconium, ruthenium, rhodium, and the like,an oxide, a nitride, or an oxynitride composed mainly of silicon, anoxide, a nitride, or an oxynitride composed mainly of a transition metalsilicide, or the like.

On the light-shielding layer containing the transition metal andsilicon, use is made of the front-surface antireflection layercontaining particularly the same silicon, and therefore, it is possibleto obtain the light-shielding film with excellent properties in maskpattern processing and, further, using the material containingmolybdenum and silicon, further excellent processing properties can beachieved.

The light-shielding film preferably comprises a back-surfaceantireflection layer formed under and in contact with thelight-shielding layer and containing at least one of oxygen and nitrogenand silicon (including a silicide compound). With this structure, theantireflection can be achieved on the back side (light-transmittingsubstrate side) of the light-shielding film. Further, since all thelayers, i.e. the front-surface antireflection layer, the light-shieldinglayer, and the back-surface antireflection layer, forming thelight-shielding film are each made of the material composed mainly ofsilicon, it is possible to obtain the light-shielding film withexcellent properties in mask pattern processing.

The front-surface antireflection layer and the back-surfaceantireflection layer may each be made of a material containing atransition metal, silicon, and at least one of oxygen and nitrogen(including a transition metal silicide compound) and the transitionmetals cited for the light-shielding layer are usable.

The thickness of the light-shielding film is preferably 60 nm or less.The front-surface antireflection layer preferably contains molybdenum,silicon, and at least one of oxygen and nitrogen, wherein the molybdenumcontent is preferably higher than 0 at % and 10 at % or less.

The present inventors have found that, by combining the light-shieldinglayer with a relatively high Mo content and the antireflection layerwith a relatively low Mo content, it is possible to form the layerstructure of the light-shielding film that satisfies the requirements inboth optical properties and chemical resistance.

When the Mo content of the antireflection layer is in theabove-mentioned range, the following functions and effects are obtained.

1) As compared with compositions which fall outside the scope of thisinvention, the antireflection layer is relatively excellent in chemicalresistance (cleaning resistance).

2) As compared with compositions which fall outside the scope of thisinvention, the antireflection layer is relatively excellent in heattreatment resistance. Specifically, the antireflection layer with a Mocontent in the above-mentioned range is prevented from becoming cloudydue to a heat treatment or prevented from the occurrence of degradationin front-surface reflectance distribution due to a heat treatment.

As the front-surface antireflection layer or the back-surfaceantireflection layer made of the material containing the transitionmetal, silicon, and at least one of oxygen and nitrogen, there can becited MoSiON, MoSiO, MoSiN, MoSiOC, MoSiOCN, or the like. Among them,MoSiO or MoSiON is preferable in terms of the chemical resistance andthe heat resistance while MoSiON is preferable in terms of the blankdefect quality.

If Mo is increased in MoSiON, MoSiO, MoSiN, MoSiOC, MoSiOCN, or the likebeing the antireflection layer, the cleaning resistance, particularlythe resistance to alkali (aqueous ammonia, etc.) or hot water,decreases. From this point of view, it is preferable to minimize Mo inMoSiON, MoSiO, MoSiN, MoSiOC, MoSiOCN, or the like being theantireflection layer.

It has been found that, upon carrying out a heat treatment (annealing)at a high temperature for the purpose of stress control, if the Mocontent is high, a phenomenon that a film surface is clouded white(becomes cloudy) occurs. This is considered to be because MoO isprecipitated on the surface. In terms of avoiding such a phenomenon, thecontent of Mo in MoSiON, MoSiO, MoSiN, MoSiOC, MoSiOCN, or the likebeing the antireflection layer is preferably less than 10 at %. However,if the Mo content is too low, abnormal discharge becomes significant inDC sputtering so that the defect occurrence frequency increases.Therefore, it is preferable to contain Mo in a range capable of carryingout the sputtering normally. According to another film formingtechnique, there is a case where the film formation is enabled withoutcontaining Mo.

The MoSi light-shielding layer is freely controllable in tensile stressand compressive stress by the Ar gas pressure, the He gas pressure, anda heat treatment. For example, by controlling the film stress of theMoSi light-shielding layer to be a tensile stress, it is possible toachieve balance with the compressive stress of the antireflection layer(e.g. MoSiON). That is, it is possible to cancel the stresses of therespective layers forming the light-shielding film and thus to reducethe film stress of the light-shielding film as much as possible (tosubstantially zero).

It is preferable to provide an etching mask film which is formed aboveand in contact with the light-shielding film and made of a materialcomposed mainly of chromium.

This is for achieving a reduction in thickness of a resist.

The etching mask film is preferably formed of a material composed mainlyof one of chromium nitride, chromium oxide, chromium oxynitride, andchromium oxycarbonitride.

This is because the etching selectivity is high with respect to theantireflection layer, formed under and in contact with the etching maskfilm, the light-shielding layer, and so on each being made of thematerial containing molybdenum and silicon, and therefore, the etchingmask film, which has become unnecessary, can be removed without damagingthe other layers.

As the etching mask film, use can be made of a material such as, forexample, chromium alone or a material containing chromium and at leastone kind of element from among oxygen, nitrogen, carbon, and hydrogen(material containing Cr). As a film structure of the etching mask film,use is often made of a single layer made of the above-mentioned filmmaterial, but use can also be made of a plural-layer structure. In thecase of the plural-layer structure, it is possible to use a plural-layerstructure formed with different compositions stepwise or a filmstructure in which the composition changes continuously.

Among them described above, chromium oxycarbonitride (CrOCN) ispreferable as the material of the etching mask film in terms of stresscontrollability (low-stress film can be formed).

The thickness of the etching mask film is preferably 5 nm to 30 nm.

A photomask can be manufactured using the above-mentioned photomaskblank.

For dry-etching the MoSi-based thin film (light-shielding film) in themanufacture of the photomask, use can be made of, for example, afluorine-based gas such as SF₆, CF₄, C₂F₆, or CHF₃, a mixed gas of sucha fluorine-based gas and He, H₂, N₂, Ar, C₂H₄, O₂ or the like, achlorine-based gas such as Cl₂ or CH₂Cl₂, or a mixed gas of such achlorine-based gas and He, H₂, N₂, Ar, C₂H₄, or the like.

For dry-etching the chromium-based thin film (etching mask film), it ispreferable to use a dry etching gas in the form of a chlorine-based gasor in the form of a mixed gas containing a chlorine-based gas and anoxygen gas. This is because if the chromium-based thin film made of thematerial containing chromium and the elements such as oxygen and/ornitrogen is dry-etched using the above-mentioned dry etching gas, it ispossible to increase the dry etching rate and thus to shorten the dryetching time so that a light-shielding film pattern with an excellentcross-sectional shape can be formed. As the chlorine-based gas for useas the dry etching gas, there can be cited, for example, Cl₂, SiCl₄,HCl, CCl₄, CHCl₃, or the like.

A synthetic quartz substrate can be cited as the light-transmittingsubstrate for use in the manufacture of the photomask blank.

The photomask blank includes an aspect in which a resist film is formedon the etching mask film. The photomask blank may be a binary photomaskblank which does not use the phase shift effect, or a resist-coated maskblank. Alternatively, the photomask blank may be a halftone phase shiftmask blank having a phase shift film between a light-transmittingsubstrate and a light-shielding film.

The phase shift film can have the same structure as conventional and isformed of, for example, a material comprising MoSiN, MoSiON, or thelike.

Further, an etching stopper film having etching resistance to thelight-shielding film or the phase shift film may be provided between thelight-transmitting substrate and the light-shielding film or between thephase shift film and the light-shielding film. The etching stopper filmis preferably in the form of a Cr-based material film like an etchingmask film because, upon etching the etching stopper film, the etchingmask film can be simultaneously stripped.

The photomask may be a binary photomask which does not use the phaseshift effect and, among phase shift masks which use the phase shifteffect, the photomask may be a halftone phase shift mask, a Levensonphase shift mask, or an enhancer mask. The photomask may be a reticle.

The photomask adapted to be applied with exposure light having awavelength of 200 nm or less may be a photomask for ArF excimer laserexposure.

In the meantime, with respect to the photomask manufactured from theabove-mentioned photomask blank, if it is considered to increase thenumber of times of use (use longer) as compared with a conventionalphotomask, the number of times of cleaning of the photomask during itsuse life also increases and, therefore, it is assumed that the film lossamount of the front-surface antireflection layer due to the cleaningduring the use life also increases. Taking this point into account,conditions for selecting a material of the front-surface antireflectionlayer should be set such that the material is adapted to provide afront-surface reflectance of a predetermined value or less for theexposure light and has a property capable of controlling the changewidth of the front-surface reflectance at the exposure wavelength to bewithin 2% when the thickness of the front-surface antireflection layeris changed (reduced) in the range of 5 nm, and a selection should bemade of the material having a refractive index n and an extinctioncoefficient k that satisfy the conditions.

In the case where the front-surface reflectance for the exposure lightis set to 30%, when a study is made of a material of the front-surfaceantireflection layer satisfying the above-mentioned conditions by thesame technique on the basis of the respective graphs in FIGS. 3 to 8,there is no material that satisfies the conditions in a material groupwith a refractive index n of 1.8 and, even if slightly exceeding 1.8,there is no material that satisfies the conditions. In a material groupwith a refractive index n of 2.1, there are materials that satisfy theconditions. In a material group with a refractive index of 3.0, there isno material that satisfies the conditions and, even if falling slightlybelow 3.0, the conditions are not satisfied. In a material group with arefractive index of 2.7, there are materials that satisfy theconditions.

On the other hand, in a material group with an extinction coefficient kof 0.3, there is no material that satisfies the conditions and, even ifslightly exceeding 0.3, there is no material that satisfies theconditions. In a material group with an extinction coefficient k of 0.6,there are materials that satisfy the conditions. In a material groupwith an extinction coefficient k of 1.8, there is no material thatsatisfies the conditions and, even if falling slightly below 1.8, theconditions are not satisfied. In a material group with an extinctioncoefficient k of 1.5, there are materials that satisfy the conditions.From the study described above, it is seen that, as a material which isused as the front-surface antireflection layer and satisfies theabove-mentioned conditions, a selection may be made of a material havinga refractive index n of 2.1 or more and 2.7 or less and an extinctioncoefficient k of 0.6 or more and 1.5 or less.

In the case where the front-surface reflectance is set to 25% which is amore preferable condition, when a study is made by the same techniquewith reference to FIGS. 3 to 8, it is seen that, as a material of thefront-surface antireflection layer satisfying the above-mentionedconditions, a selection may be made of a material having a refractiveindex n of 2.1 or more and 2.7 or less and an extinction coefficient kof 0.6 or more and 1.2 or less.

When the front-surface reflectance for the exposure light is 25% orless, conditions for selecting a material of the front-surfaceantireflection layer can be set such that the material has a propertycapable of controlling the change width of the front-surface reflectanceat the exposure wavelength to be within 3% when the thickness of thefront-surface antireflection layer is changed (reduced) in the range of5 nm, and a selection can be made of the material having a refractiveindex n and an extinction coefficient k that satisfy the conditions.

When a study is made of a material of the front-surface antireflectionlayer satisfying the above-mentioned conditions by the same technique onthe basis of the respective graphs in FIGS. 11 to 16, there is nomaterial that satisfies the conditions in material groups withrefractive indices n of 1.4 and 1.7. In a material group with arefractive index n of 2.0, there are materials that satisfy theconditions in the ranges where the extinction coefficient k is 1.0 andthe thickness is 14 to 20 nm. In a material group with a refractiveindex n of 2.31, there are materials that satisfy the conditions in theranges where the extinction coefficient k is 0.4 to 1.3 and thethickness is 10 to 20 nm. In a material group with a refractive index nof 2.6, there are materials that satisfy the conditions in the rangeswhere the extinction coefficient k is 0.4 to 1.0 and the thickness is 8to 20 nm. In a material group with a refractive index of 2.9, there arematerials that satisfy the conditions in the ranges where the extinctioncoefficient k is 0.4 to 1.0 and the thickness is 6 to 13 nm.

On the other hand, in a material group with an extinction coefficient kof 0.4, there are materials that satisfy the conditions in the rangeswhere the refractive index n is 2.31 to 2.9 and the thickness is 7 to 18nm. In a material group with an extinction coefficient k of 0.7, thereare materials that satisfy the conditions in the ranges where therefractive index n is 2.31 to 2.9 and the thickness is 6 to 20 nm. In amaterial group with an extinction coefficient k of 1.0, there arematerials that satisfy the conditions in the ranges where the refractiveindex n is 2.0 to 2.9 and the thickness is 6 to 20 nm. In a materialgroup with an extinction coefficient k of 1.3, there are materials thatsatisfy the conditions in the ranges where the refractive index n is2.31 and the thickness is 15 to 20 nm. In material groups withextinction coefficients k of 1.6 and 1.9, there is no material thatsatisfies the conditions.

From the study described above, it is seen that, as a material which isused as the front-surface antireflection layer and satisfies theabove-mentioned conditions, a selection may be made of a material havinga refractive index n of 2.0 or more and 2.9 or less and an extinctioncoefficient k of 0.4 or more and 1.3 or less.

Further, when the front-surface reflectance for the exposure light is25% or less, conditions are preferably set such that a material has aproperty capable of controlling the change width of the front-surfacereflectance at the exposure wavelength to be within 2% when thethickness of the front-surface antireflection layer is changed (reduced)in the range of 5 nm.

When a study is made of a material of the front-surface antireflectionlayer satisfying the above-mentioned conditions on the basis of therespective graphs in FIGS. 11 to 16, there is no material that satisfiesthe conditions in material groups with refractive indices n of 1.4 and1.7. In a material group with a refractive index n of 2.0, there arematerials that satisfy the conditions in the ranges where the extinctioncoefficient k is 1.0 and the thickness is 15 to 20 nm. In a materialgroup with a refractive index n of 2.31, there are materials thatsatisfy the conditions in the ranges where the extinction coefficient kis 0.4 to 1.3 and the thickness is 11 to 20 nm. In a material group witha refractive index n of 2.6, there are materials that satisfy theconditions in the ranges where the extinction coefficient k is 0.7 to1.0 and the thickness is 8 to 17 nm. In a material group with arefractive index of 2.9, there are materials that satisfy the conditionsin the ranges where the extinction coefficient k is 1.0 and thethickness is 6 to 12 nm.

On the other hand, in a material group with an extinction coefficient kof 0.4, there are materials that satisfy the conditions in the rangeswhere the refractive index n is 2.31 and the thickness is 12 to 18 nm.In a material group with an extinction coefficient k of 0.7, there arematerials that satisfy the conditions in the ranges where the refractiveindex n is 2.31 to 2.6 and the thickness is 8 to 20 nm. In a materialgroup with an extinction coefficient k of 1.0, there are materials thatsatisfy the conditions in the ranges where the refractive index n is 2.0to 2.9 and the thickness is 6 to 20 nm. In a material group with anextinction coefficient k of 1.3, there are materials that satisfy theconditions in the ranges where the refractive index n is 2.31 and thethickness is 15 to 20 nm. In material groups with extinctioncoefficients k of 1.6 and 1.9, there is no material that satisfies theconditions.

From the study described above, it is seen that, as a material which isused as the front-surface antireflection layer and satisfies theabove-mentioned conditions, a selection may be made of a material havinga refractive index n of 2.0 or more and 2.9 or less and an extinctioncoefficient k of 0.4 or more and 1.3 or less.

Hereinbelow, Examples of this invention will be shown. In each Example,films such as a light-shielding film and an etching film were formed bya sputtering method as a film forming method using a DC magnetronsputtering apparatus as a sputtering apparatus. However, for carryingout this invention, there is no particular limitation to such a filmforming method and film forming apparatus and use may be made of anothertype of sputtering apparatus such as an RF magnetron sputteringapparatus.

EXAMPLE 1 Optical Simulation and Selection of Front-SurfaceAntireflection Layer

A synthetic quartz substrate having a 6-inch square size with athickness of 0.25 inches was used as a light-transmitting substrate 1and, on this light-transmitting substrate 1, a MoSi film was formedunder the same conditions as those for a light-shielding layer of alight-shielding film.

Specifically, using a target of Mo:Si=21:79 (at % ratio) and using Arand He (gas flow rate ratio Ar:He=20:120) at a sputtering gas pressureof 0.3 Pa, a light-shielding layer comprising molybdenum and silicon wasformed to a thickness of 30 nm by setting the power of the DC powersupply to 2.0 kW.

Then, the refractive index n and the extinction coefficient k of theformed light-shielding layer were measured using an optical thin-filmproperty measuring apparatus n&k 1280 (manufactured by n&k Technology,Inc.). It was confirmed that this light-shielding layer had a refractiveindex n of 2.42 and an extinction coefficient k of 2.89 and thus hadhigh light-shielding performance.

Then, based on the measured refractive index n and extinctioncoefficient k of the light-shielding layer, optical simulations werecarried out for selecting a front-surface antireflection layer to beformed on an upper surface of the light-shielding layer. The opticalsimulations were carried out by changing the refractive index n (in 6levels of 1.5, 1.8, 2.1, 2.36, 2.7, and 3.0), the extinction coefficientk (in 6 levels of 0.3, 0.6, 0.9, 1.2, 1.5, and 1.8), and the thicknessof front-surface antireflection layers as variable parameters.

The results thereof are shown in FIGS. 3 to 8 (graphs 1 to 6).

From the graphs 1 to 6, it is seen that if n and k of a front-surfaceantireflection layer 13 differ, a change in front-surface reflectance(slope of a curve in the graph) with respect to a change in thicknessdiffers considerably.

In this Example, a light-shielding film has a front-surface reflectanceof 25% or less and a front-surface antireflection layer is such that thechange width of the front-surface reflectance falls within 2% when thethickness of the front-surface antireflection layer is changed in therange of 2 nm, and a selection is made of a material with n and k havingsuch a property.

An additional condition desired for the front-surface antireflectionlayer is that its extinction coefficient k is as high as possible. Thisis because if the extinction coefficient k of the material is high, thelight-shielding performance also becomes high, and therefore, even ifthe thickness of the light-shielding layer is made thin, it is possibleto ensure an OD of a predetermined value or higher over the entirelight-shielding film, thus achieving a reduction in thickness of thelight-shielding film.

Taking these conditions into account, use is made of a thickness rangeof 13 nm to 15 nm in a curve (n=2.36, k=1.2) in the graph 4 shown inFIG. 6. As is also seen from FIG. 6 (graph 4), assuming that a maskblank is manufactured by forming a front-surface antireflection layerwith a thickness of 15 nm and that the thickness is changed in the rangeof 2 nm due to mask cleaning or the like in the use after themanufacture of a photomask, the change width of the front-surfacereflectance becomes 1.1% in simulation. Further, the front-surfacereflectance after the film loss is 21.1% so that it is possible toensure 25% or less. In addition, when the front-surface antireflectionlayer having this property is used, even if the thickness of alight-shielding layer is 30 nm and the thickness of a back-surfaceantireflection layer is 7 nm, it is possible to ensure an OD of apredetermined value or higher over the entire light-shielding film andthus to achieve a reduction in thickness of the light-shielding film.

In the case where it is allowed to enhance the light-shieldingperformance by somewhat increasing the thickness of the light-shieldinglayer, it is possible to use a material with a lower extinctioncoefficient k (e.g. k=0.3 etc.).

(Manufacture of Photomask Blank)

(Formation of Light-Shielding Film)

A photomask blank was actually manufactured using a light-shielding filmstructure which was selected as a result of the study described above.Using a synthetic quartz substrate having a 6-inch square size with athickness of 0.25 inches as a light-transmitting substrate 1, a MoSiONfilm 11 (back-surface antireflection layer), a MoSi (light-shieldinglayer) 12, and a MoSiON film (front-surface antireflection layer) 13were respectively formed as a light-shielding film 10 on thelight-transmitting substrate 1 (FIG. 1).

Specifically, using a target of Mo:Si=21:79 (at % ratio) and using Ar,O₂, N₂, and He (gas flow rate ratio Ar:O₂:N₂:He=5:4:49:42) at asputtering gas pressure of 0.2 Pa, a film comprising molybdenum,silicon, oxygen, and nitrogen (Mo: 0.3 at %, Si: 24.6 at %, O: 22.5 at%, N: 52.6 at %) (n: 2.39, k: 0.78) was formed to a thickness of 7 nm bysetting the power of the DC power supply to 3.0 kW.

Then, using a target of Mo:Si=21:79 (at % ratio) and using Ar and He(gas flow rate ratio Ar:He=20:120) at a sputtering gas pressure of 0.3Pa, a film comprising molybdenum and silicon (Mo: 21.0 at %, Si: 79 at%) (n: 2.42, k: 2.89) was formed to a thickness of 30 nm by setting thepower of the DC power supply to 2.0 kW.

Then, using a target of Mo:Si=4:96 (at % ratio) and using Ar, O₂, N₂,and He (gas flow rate ratio Ar:O₂:N₂:He=6:5:11:16) at a sputtering gaspressure of 0.1 Pa, a film comprising molybdenum, silicon, oxygen, andnitrogen (Mo: 1.6 at %, Si: 38.8 at %, O: 18.8 at %, N: 41.1 at %) (n:2.36, k: 1.20) was formed to a thickness of 15 nm by setting the powerof the DC power supply to 3.0 kW. The total thickness of thelight-shielding film 10 was set to 52 nm. The optical density (OD) ofthe light-shielding film 10 was 3 at a wavelength 193 nm of ArF excimerlaser exposure light.

Then, the above-mentioned substrate was heat-treated (annealed) at 450°C. for 30 minutes, thereby reducing the film stress.

(Formation of Etching Mask Film)

Then, an etching mask film 20 was formed on the light-shielding film 10(FIG. 1). Specifically, using a chromium target and using Ar, CO₂, N₂,and He (gas flow rate ratio AnCO₂:N₂:He=21:37:11:31) at a sputtering gaspressure of 0.2 Pa, a CrOCN film (Cr content in the film: 33 at %) wasformed to a thickness of 15 nm by setting the power of the DC powersupply to 1.8 kW. In this event, the CrOCN film was annealed at atemperature lower than the annealing temperature of the MoSilight-shielding film, thereby adjusting the stress of the CrOCN film tobe as small as possible (preferably, substantially zero) withoutaffecting the film stress of the MoSi light-shielding film.

In this manner, a photomask blank formed with the light-shielding filmfor ArF excimer laser exposure was obtained.

The elements of the thin films were analyzed by the Rutherfordbackscattering spectrometry.

(Manufacture of Photomask)

On the etching mask film 20 of the photomask blank, a chemicallyamplified positive resist 50 for electron beam writing (exposure)(PRL009: manufactured by FUJIFILM Electronic Materials Co., Ltd.) wascoated to a thickness of 100 nm by a spin-coating method (FIG. 1, FIG.2(1)).

Then, using an electron beam writing apparatus, a desired pattern (40nm, 45 nm, 50 nm, 55 nm, 60 nm line and space) was written on the resistfilm 50 and, thereafter, development was carried out using apredetermined developer, thereby forming a resist pattern 50 a (FIG.2(2)).

Then, using the resist pattern 50 a as a mask, the etching mask film 20was dry-etched (FIG. 2(3)). A mixed gas of Cl₂ and O₂ (Cl₂:O₂=4:1) wasused as a dry etching gas.

Then, the remaining resist pattern 50 a was stripped and removed by achemical solution.

Then, using an etching mask film pattern 20 a as a mask, thelight-shielding film 10 was dry-etched using a mixed gas of SF₆ and He,thereby forming a light-shielding film pattern 10 a (FIG. 2(4)).

Then, the etching mask film pattern 20 a was stripped by dry etchingwith a mixed gas of Cl₂ and O₂ (FIG. 2(5)) and then predeterminedcleaning was carried out, thereby obtaining a photomask 100.

(Evaluation)

For the photomask thus obtained, the front-surface reflectance (% R),the back-surface reflectance (% Rb), and the OD (% T) upon irradiationof light having a wavelength of 193 nm to 800 nm were measured using aspectrophotometer U-4100 (manufactured by Hitachi High-TechnologiesCorporation). The results were obtained as shown in FIG. 10. It was seenthat the properties (front-surface reflectance % R: 20.8%, back-surfacereflectance % Rb: 28.1%) for ArF exposure light (wavelength 193 nm) foruse with the photomask were excellent and further that the properties ata wavelength of inspection light (e.g. 250 nm to 433 nm) for use in amask inspection apparatus or the like were also excellent.

Then, this photomask was cleaned with ozone water normally used inphotomask cleaning, thereby reducing the thickness of the front-surfaceantireflection layer 13 by 2 nm. The front-surface reflectance wasmeasured in the same manner and it was 22.1%, and therefore, the changeamount of the front-surface reflectance due to the film loss was 1.3%and thus was suppressed within 2%.

EXAMPLE 2 Selection of Front-Surface Antireflection Layer

This Example 2 aims at providing a light-shielding film having afront-surface reflectance of 25% or less and at providing afront-surface antireflection layer such that the change width of thefront-surface reflectance falls within 2% when the thickness of thefront-surface antireflection layer is changed in the range of 5 nm,which is a stricter condition, and a selection was made of a materialwith n and k having such a property.

Taking these conditions into account, use is made of a thickness rangeof 17 nm to 12 nm in a curve (n=2.36, k=1.2) in the graph 4 shown inFIG. 6. As is also seen from FIG. 6 (graph 4), assuming that a maskblank is manufactured by forming a front-surface antireflection layerwith a thickness of 17 nm and that the thickness is changed in the rangeof 5 nm due to mask cleaning or the like in the use after themanufacture of a photomask, the change width of the front-surfacereflectance becomes 1.8% in simulation. Further, the front-surfacereflectance after the film loss is 22.1% so that it is possible toensure 25% or less.

(Manufacture of Photomask Blank and Photomask)

A photomask blank was actually manufactured using a light-shielding filmstructure which was selected as a result of the study described above.The photomask blank had the same structure as the photomask blank ofExample 1 except that the thickness of a front-surface antireflectionlayer was set to 17 nm, and was manufactured by the same processes as inExample 1. Further, a photomask was manufactured from the manufacturedphotomask blank in the same manner as in Example 1.

(Evaluation)

For the photomask thus obtained, the front-surface reflectance (% R) andthe back-surface reflectance (% Rb) upon irradiation of ArF exposurelight (wavelength 193 nm) were measured using a spectrophotometer U-4100(manufactured by Hitachi High-Technologies Corporation). Excellentresults were obtained such that the front-surface reflectance % R was20.2% and the back-surface reflectance % Rb was 28.1%.

Then, this photomask was cleaned with ozone water normally used inphotomask cleaning, thereby reducing the thickness of the front-surfaceantireflection layer 13 by 5 nm. The front-surface reflectance wasmeasured in the same manner and it was 22.1%, and therefore, the changeamount of the front-surface reflectance due to the film loss was 1.9%and thus was suppressed within 2%.

EXAMPLE 3 Optical Simulation and Selection of Front-SurfaceAntireflection Layer

This Example was the same as Example 1 except that the light-shieldinglayer was changed from the MoSi film to a MoSiN film so that alight-shielding film had a two-layer structure.

On a light-transmitting substrate, a MoSiN film was formed under thesame conditions as those for a light-shielding layer of alight-shielding film.

Specifically, using a target of Mo:Si=21:79 (at % ratio) and using Arand N₂ (gas flow rate ratio Ar:N₂=25:28) at a sputtering gas pressure of0.07 Pa, a light-shielding layer comprising molybdenum, silicon, andnitrogen was formed to a thickness of 50 nm by setting the power of theDC power supply to 2.1 kW.

Then, the refractive index n and the extinction coefficient k of theformed light-shielding layer were measured using an optical thin-filmproperty measuring apparatus n&k 1280 (manufactured by n&k Technology,Inc.). It was confirmed that this light-shielding layer had a refractiveindex n of 2.42 and an extinction coefficient k of 1.91 and thus hadhigh light-shielding performance.

Then, based on the measured refractive index n and extinctioncoefficient k of the light-shielding layer, optical simulations werecarried out for selecting a front-surface antireflection layer to beformed on an upper surface of the light-shielding layer. The opticalsimulations were carried out by changing the refractive index n (in 6levels of 1.4, 1.7, 2.0, 2.31, 2.6, and 2.9), the extinction coefficientk (in 6 levels of 0.4, 0.7, 1.0, 1.3, 1.6, and 1.9), and the thicknessof front-surface antireflection layers as variable parameters.

The results thereof are shown in FIGS. 11 to 16 (graphs 7 to 12).

From the graphs 7 to 12, it is seen that if n and k of the front-surfaceantireflection layer differ, a change in front-surface reflectance(slope of a curve in the graph) with respect to a change in thicknessdiffers considerably.

In this Example, a light-shielding film has a front-surface reflectanceof 25% or less and a front-surface antireflection layer is such that thechange width of the front-surface reflectance falls within 3% when thethickness of the front-surface antireflection layer is changed in therange of 2 nm, and a selection is made of a material with n and k havingsuch a property.

An additional condition desired for the front-surface antireflectionlayer is that its extinction coefficient k is as high as possible. Thisis because if the extinction coefficient k of the material is high, thelight-shielding performance also becomes high, and therefore, even ifthe thickness of the light-shielding layer is made thin, it is possibleto ensure an OD of a predetermined value or higher over the entirelight-shielding film, thus achieving a reduction in thickness of thelight-shielding film.

Taking these conditions into account, use is made of a thickness rangeof 8 nm to 10 nm in a curve (n=2.31, k=1.0) in the graph 10 shown inFIG. 14. As is also seen from FIG. 14 (graph 10), assuming that a maskblank is manufactured by forming a front-surface antireflection layerwith a thickness of 10 nm and that the thickness is changed in the rangeof 2 nm due to mask cleaning or the like in the use after themanufacture of a photomask, the change width of the front-surfacereflectance becomes 2.5% in simulation. Further, the front-surfacereflectance after the film loss is 23.8% so that it is possible toensure 25% or less. In addition, when the front-surface antireflectionlayer having this property is used, it is possible to ensure an OD of apredetermined value or higher over the entire light-shielding film andthus to achieve a reduction in thickness of the light-shielding film.

In the case where it is allowed to enhance the light-shieldingperformance by somewhat increasing the thickness of the light-shieldinglayer, it is possible to use a material with a lower extinctioncoefficient k (e.g. k=0.4 etc.).

(Manufacture of Photomask Blank and Photomask)

A photomask blank was actually manufactured using a light-shielding filmstructure which was selected as a result of the study described above.This Example differed from Example 1 in that the light-shielding layerwas changed from the MoSi film to a MoSiN film and that alight-shielding film had a two-layer structure provided with noback-surface antireflection layer. That is, a MoSiN film(light-shielding layer) and a MoSiON film (front-surface antireflectionlayer) were respectively formed as a light-shielding film on alight-transmitting substrate.

Specifically, using a target of Mo:Si=21:79 (at % ratio) and using Arand N₂ (gas flow rate ratio Ar:N₂=25:28) at a sputtering gas pressure of0.07 Pa, a film comprising molybdenum, silicon, and nitrogen (Mo: 14.7at %, Si: 56.2 at %, N: 29.1 at %) (n: 2.42, k: 1.91) was formed to athickness of 50 nm by setting the power of the DC power supply to 2.1kW.

Then, using a target of Mo:Si=4:96 (at % ratio) and using Ar, O₂, N₂,and He (gas flow rate ratio Ar:O₂:N₂:He=6:3:11:17) at a sputtering gaspressure of 0.1 Pa, a film comprising molybdenum, silicon, oxygen, andnitrogen (Mo: 2.6 at %, Si: 57.1 at %, O: 15.9 at %, N: 24.4 at %) (n:2.31, k: 1.00) was formed to a thickness of 10 nm by setting the powerof the DC power supply to 3.0 kW.

The total thickness of the light-shielding film was set to 60 nm. Theoptical density (OD) of the light-shielding film was 3 at a wavelength193 nm of ArF excimer laser exposure light.

Then, the above-mentioned substrate was heat-treated (annealed) at 450°C. for 30 minutes, thereby reducing the film stress.

Then, an etching mask film and a chemically amplified positive resistfor electron beam writing (exposure) which were the same as those inExample 1 were formed on the light-shielding film.

Then, a photomask was obtained in the same manner as in Example 1.

(Evaluation)

For the photomask thus obtained, the front-surface reflectance (% R) andthe back-surface reflectance (% Rb) upon irradiation of ArF exposurelight (wavelength 193 nm) were measured using a spectrophotometer U-4100(manufactured by Hitachi High-Technologies Corporation). Excellentresults were obtained such that the front-surface reflectance % R was15.7% and the back-surface reflectance % Rb was 32.7%.

Then, this photomask was cleaned with ozone water normally used inphotomask cleaning, thereby reducing the thickness of the front-surfaceantireflection layer by 2 nm. The front-surface reflectance was measuredin the same manner and it was 18.3%, and therefore, the change amount ofthe front-surface reflectance due to the film loss was 2.6% and thus wassuppressed within 3%.

EXAMPLE 4 Selection of Front-Surface Antireflection Layer

This Example 4 aims at providing a light-shielding film having afront-surface reflectance of 25% or less and at providing afront-surface antireflection layer such that the change width of thefront-surface reflectance falls within 2% when the thickness of thefront-surface antireflection layer is changed in the range of 5 nm,which is a stricter condition, and a selection was made of a materialwith n and k having such a property.

Taking these conditions into account, use is made of a thickness rangeof 11 nm to 16 nm in a curve (n=2.31, k=1.0) in the graph 10 shown inFIG. 14. As is also seen from FIG. 14 (graph 10), assuming that a maskblank is manufactured by forming a front-surface antireflection layerwith a thickness of 16 nm and that the thickness is changed in the rangeof 5 nm due to mask cleaning or the like in the use after themanufacture of a photomask, the change width of the front-surfacereflectance becomes 1.9% in simulation. Further, the front-surfacereflectance after the film loss is 20.4% so that it is possible toensure 25% or less.

(Manufacture of Photomask Blank and Photomask)

A photomask blank was actually manufactured using a light-shielding filmstructure which was selected as a result of the study described above.The photomask blank had the same structure as the photomask blank ofExample 3 except that the thickness of a front-surface antireflectionlayer was set to 16 nm and that the thickness of a light-shielding layerwas set to 44 nm, and was manufactured by the same processes as inExample 3. Further, a photomask was manufactured from the manufacturedphotomask blank in the same manner as in Example 1.

(Evaluation)

For the photomask thus obtained, the front-surface reflectance (% R) andthe back-surface reflectance (% Rb) upon irradiation of ArF exposurelight (wavelength 193 nm) were measured using a spectrophotometer U-4100(manufactured by Hitachi High-Technologies Corporation). Excellentresults were obtained such that the front-surface reflectance % R was19.3% and the back-surface reflectance % Rb was 31.5%.

Then, this photomask was cleaned with ozone water normally used inphotomask cleaning, thereby reducing the thickness of the front-surfaceantireflection layer by 5 nm. The front-surface reflectance was measuredin the same manner and it was 22.1%, and therefore, the change amount ofthe front-surface reflectance due to the film loss was 1.8% and thus wassuppressed within 2%.

While this invention has been described with reference to the Examples,the technical scope of the invention is not limited to the scope of thedescription of the above-mentioned Examples. It is obvious to a personskilled in the art that various changes or improvements can be added tothe above-mentioned Examples. It is clear from the description of claimsthat the modes added with such changes or improvements can also beincluded in the technical scope of this invention.

DESCRIPTION OF SYMBOLS

-   -   1 light-transmitting substrate    -   10 light-shielding film    -   11 back-surface antireflection layer    -   12 light-shielding layer    -   13 front-surface antireflection layer    -   20 etching mask film    -   50 resist film    -   100 photomask

The invention claimed is:
 1. A photomask blank for use in manufacturinga photomask adapted to be applied with exposure light having awavelength of 200 nm or less, wherein the photomask blank comprises alight-transmitting substrate and a light-shielding film formed on thelight-transmitting substrate, the light-shielding film comprises alight-shielding layer containing a transition metal and silicon and afront-surface antireflection layer formed above and in contact with thelight-shielding layer and made of a material containing a transitionmetal, silicon, and at least one of oxygen and nitrogen, and thefront-surface antireflection layer has a refractive index n being 1.4 ormore and 2.9 or less and an extinction coefficient k being 0.4 or moreand 1.3 or less.
 2. The photomask blank according to claim 1, whereinthe front-surface antireflection layer has a thickness of 20 nm or less.3. The photomask blank according to claim 1, wherein the transitionmetal of the front-surface antireflection layer has a content beinghigher than 0 at % and 10 at % or less.
 4. The photomask blank accordingto claim 1, wherein the transition metal of the front-surfaceantireflection layer is selected from molybdenum, tantalum, tungsten,titanium, chromium, hafnium, nickel, vanadium, zirconium, ruthenium, andrhodium.
 5. The photomask blank according to claim 1, wherein thefront-surface antireflection layer is formed of a material selected fromMoSiON, MoSiO, MoSiN, MoSiOC, and MoSiOCN.
 6. The photomask blankaccording to claim 1, wherein the light-shielding layer has a thicknessof 40 nm or more and 50 nm or less.
 7. The photomask blank according toclaim 1, wherein the transition metal of the light-shielding layer isselected from molybdenum, tantalum, tungsten, titanium, chromium,hafnium, nickel, vanadium, zirconium, ruthenium, and rhodium.
 8. Thephotomask blank according to claim 1, wherein the light-shielding layeris formed of a material substantially comprising molybdenum, silicon,and nitrogen.
 9. The photomask blank according to claim 8, wherein thenitrogen of the light-shielding layer has a content being less than 40at %.
 10. The photomask blank according to claim 1, wherein thelight-shielding film has a thickness of 60 nm or less.
 11. The photomaskblank according to claim 1, further comprising an etching mask formed onthe light-shielding film.
 12. The photomask blank according to claim 11,wherein the etching mask is formed of chromium alone or a materialcontaining chromium and at least one kind of element from among oxygen,nitrogen, carbon, and hydrogen.
 13. The photomask blank according toclaim 1, which is a resist-coated mask blank.
 14. A photomask, which ismanufactured by using the photomask blank according to claim
 1. 15. Amethod of manufacturing a photomask, comprising using the photomaskblank according to claim
 1. 16. A method of manufacturing asemiconductor device, comprising transferring a pattern of the photomaskaccording to claim 14.